Ratiometric converter types of circuits receive as inputs a sense signal and a reference signal and provide an output signal which is proportional to the sense signal and inversely proportional to the reference signal. Ratiometric converters are used primarily in conjunction with ratiometric DC measurement systems. These DC measurement systems are often Wheatstone bridge circuits in which one of the resistive elements in the bridge is a transducer, such as for example a strain gauge. Such Wheatstone bridge ratiometric measurement systems are also used to measure weight, pressure, temperature, and other mechanical parameters. The system is energized by placing a DC voltage across the bridge, and the DC voltage across the bridge provides a differential reference voltage to the ratiometric converter. The voltage generated across the other two nodes of the bridge forms a differential sense voltage to the ratiometric converter. The ratiometric converter then provides an output signal which is proportional to the differential sense signal and inversely proportional to the differential reference voltage.
In most systems, the transducer is located some distance from the ratiometric converter, and in some cases over 100 meters. Any interference pickup such as power line interference, RF interference, and other types of electromagnetic noise, will corrupt the DC measurement.
In the past shields (such as coaxial cables), twisted wire pairs, and/or analog filters have been used to reduce this interference. While these procedures have been effective for most prior art systems, as higher accuracy systems are evolving (e.g. 16-bit digital systems) a better method of reducing or removing the electromagnetic interference and noise is required.